

present be considered as an internal variation, just as 

 though enlargement of mycelial disks were accompanied by a 

 progressive increase or decrease in enzyme content of one 

 terminal cells at the margin of the disk ; such variation 

 in the cell itself would be a clear case of internal varia- 

 tion, change in the nature of the fungus itself. 



As has been said, the temperature conditions were 

 always artificially maintained, with a very small degree of 

 fluctuation throughout any given culture period. Ihey dif - 

 fered . of course, from experiment to experiment, but they 

 did not vary appreciably in any case. Thus the temperature 

 conditions for any culture are clearly and definitely stated 

 by giving merely the temperature index as read or. the ther- 

 mometer scale. 



Radiation conditions are regarded as non-existent in 

 these tests. Light (and radiation of still shorter wave 

 lengths) was always excluded, and the stirring apparatus op- 

 erated to prevent any one-3ided action of long-wave radiation 

 upon the cu2 tures. 



The duration condition offers no particular difficul- 

 ty in such work as this. If the culture period or observa- 

 tion period for any culture is different from that for an- 

 other this fact i3 quantitatively 3hown by the records of 

 times of inoculation ar£ times of observation and measurement. 

 Therefore differences in this condition are easily taken into 

 quantitative account in the interpretation of growth differ - 

 erces between different cultures, in terms of their length of 



16 



